Production of acrylonitrile



ticularly those having Patented Sept. 25, 1945 UNITED STATES PATENTorrics I I I raonuo'rion fiz j nolvirama Le Roy U. Spence,

Elkins Park, 2a., auignor to hm a Haas Company, Philadelphia, Pa.

No Drawing. Application Ogtober 15, 1940;

This invention relates to a process for the manufacture of unsaturatedaliphatic nitrlles, parthe general formula: CH9=C-CN in which R is ahydrogen atom or an alkyl group, by splitting hydrogen chloride out ofthe corresponding saturated monochloro nitrlles.

The object or this invention is to provide a convenient and practicalprocess for converting moncchloro saturated aliphatic nitrlles, of theeneral formula:

i i in which R is hydrogen or an alkyl group and one 01' the X's ishydrogen and the other chlorine, into the unsaturated nitrile of theformula given above. More particularly, the object is to provide amethod for the manufacture of acrylonitrile and methacrylonitrile fromchloropropionitrile and chloroisobutyronitrlle respectively, especiallyfrom the m-OhJOl'O nitrlles.

It has been proposed to convert chlorinated saturated aliphatic nitrllesto the corresponding unsaturated nitrile by heating them to relativelyhigh temperatures which causes hydrogen .chloride to be split out of thechlorinated nitrile. Such proposal is made in U. S. Patent No. 2,174,-756. Whentreated according to this method, the chlorinated nitrllesbehave differently depending on the location of the chlorine atom. It israther difllcult to split hydrogen chloride out of the nitrlles in whichthe chlorine atom is attached to the a-carbon atom but with those inwhich the chlorine is attached to a p-carbon atom it is comparativelyeasy to do so. Thus, much higher temperatures are required to convertthe m-Ol'lIOlO saturated nitrlles to the unsaturated nitrlle than arenecessary for the corresponding conversion of the p-chloro saturatednitrlles.

It has now been found that there is also a difference in the behavior ofthe saturated aand ,B-chloro aliphatic nitrlles when treated withalkaline materials, particularly aqueous solutions of these materials.At ordinary temperatures strong alkalies, such as sodium or calciumhydroxide, will convert the p-chloronitriles practlcally quantitativelyto the corresponding unsaturated nitrile. Weaker-'alkalies such assodium bicarbonate or sodium carbonate will bring about the sameconversion at higher temperatures, especially at the boiling point ofthe solution. In

neither case is there any appreciable hydrolysis of the nitrile groupprovided the amount of alkali employed" is only slightly in excess ofthe amount required to split the hydrogen chloride out of thefi-chloronitrile. 0n the other hand, when the a=chloronitriles aretreated with strong alkali even at high temperatures no unsaturatednitrile is formed. In this case the principal reaction is thereplacementof the chlorine atom by a hydroxyl group forming thecorresponding ahydroxy nitrile. Some hydrolysis of the nitrile groupalso takes place, Weaker alkalies, such as sodium carbonate, even at thetemperature of the boiling solution do not react readily with thechlorine atom of the a-ch'lOlO nitrile so that these nitrlles can beboiled with weak alkalies without substantial change. Thus, when amixture of saturated ozand fl-chloronitriles is treated with an alkalinesolution, all of the p-chloronitrile is converted to the correspondingunsaturated nitrile whereas the a-Cl'llOlOllitlil8 remains substantiallyunchanged.

In the process of pyrolyzing 02- or ,B-chlorinated saturated nitrlles ora mixture of the two, the product obtained on condensing the gasescontains the unsaturated nitrile, any undissociated chloronitrile andthe hydrogen chloride which is split out. However, when the product iscooled to ordinary temperatures the hydrogen chloride and theunsaturated nitrile recombine. to a considerable extent to formexclusively the fl-chloro saturated nitrile. Attempts to separate anyunsaturated nitrile which may be present in such a product by fractionaldistillation were unsuccessful for the reasonthat at the boiling pointof the mixture some of the p-chloronitrile decomposes, the unsaturatednitrile and the hydrogen chloride thus formed pass over to the condenserand recombine in the condensate. It has been proposed to, remove thehydrogen chloride from the reaction product by washing with water. Thisdoes not entirely prevent the formation of the ,i-chloronitrile and,moreover, causes considerable hydrolysis 'of the nitrlles to thecorresponding amides and acids which reduces the yield 01. unsaturatednitrile.

The present invention is designed to overcome these dimculties andprovide a process whereby high yields of the unsaturated nitrile can beobtained from the a-ChlOl'OllitlilB. The process consists in heating thea-chlorom'trile to split out hydrogen chloride, condensing the productsof pyrolysis, treating the condensate with sufiicient alkaline materialto neutralize the hydrogen chloride and split out hydrogen chloride fromissuing from the the p-chloronitriles formed in the condensate andthenlfractionally distilling the material to separate the unsaturatednitrile from any unchanged a-OhlOlOl'lltlilC. In the pyrolyzing step 01'the process, the a-chloronitriles are converted to the unsaturatednitrile but, when the products are.

condensed, the hydrogen chloride and the unsaturated nitrile recombineto form the p-chloronitrile which is readily converted to the desiredunsaturated nitrile by means of alkaline substances. The startingmaterial may be pure uchloronitrile or a mixture of aand pchloronitriles such as is obtained by the vapor phase chlorination ofsaturated aliphatic nitriles described in U. S. application Serial No.353,066 filed August 1'7, 1940 which on May 19, 1942, issued as PatentNo. 2,283,237. r

The process is carried out in general as follows The pure saturatedu-chloronitriie or a mixture of c:- and p-chloronitriles is passedthrough a pyrolyzing zone at a temperature high enough to cause hydrogenchloride to be split out. This may be from about 450 to about 700 C. Theoptimal range will vary according to the nitrile employed, time ofcontact, etc. The products pyrolyzing zone are passed through acondenser to condense the normally liquid products. The condensate willcontain some unsaturated nitrile, dissolved hydrogen chloride, anyunchanged a-chloronitrile and considerable p-chloronitrile. Thecondensate is then treated with a solution or suspension of an alkalinematerial to neutralize any free hydrogen chloride and to react with thep-chloronitrile to split out hydrogen chloride. The organic and aqueouslayers of the resulting mixture are then separated and the organic layerdistilled to separate the unsaturated nitrile from the unchangeda-chloronitrile. Alternatively, the aqueous layer may be made neutraland the entire mixture fractionally distilled. In this case theunsaturated nitrile comes over as an azeotropicv mixture with water. Ineither case the a-chloronitrile recovered can be returned to thepyrolyzing step.

The alkali used to neutralize the hydrogen chloride and convert thep-chloronitrile to the unsaturated nitrile may be sodium, potassium,calcium or barium hydroxide, as well as the carbonates and bicarbonatesof these metals. These are generally employed in aqueous solutions orsuspensions. When a strong alkali, such as sodium hydroxide, or lime, isused the amount employed should be equivalent to the amount of freehydrogen chloride and the p-chloronitrile. It the solution is kept cold,a small excess or the alkali can be employed but this must beneutralized before distillation directly from the solution in order toavoid hydrolysis of the nitriles. When a weak alkali, such as sodiumbicarbonate or sodium carbonate, is employed, the mixture may bedistilled directly since a small excess of these does not render thesolution suificiently strongly alkaline t cause any appreciablehydrolysis. Heating or even boiling is advantageous with the weakalkalies in order to speed up the conversion of the p-chloronitrile.

As noted above, the optimal temperature for the pyrolyzing step dependsto some extent on the nature of the a-chloronitrile. In the case ofoz-OhlOl'ODl'OPiOIlitl'ilQ 5'75 to 625 C. is preferred whereas foru-chloroisobutyronitrile 500 to 575 C. gives the best results.

Catalytic materials such as activated alumina, pumice, etc. apparentlyhave little or no eflect on the reaction and do not change theproportion or a-chloronitrile which is decomposed in a single passagethrough the reaction zone. It is advantageous to use an inert packing soas'to insure more uniform temperatures in the gas stream and quartz issuitable for this purpose. The inert packing is not necessary as goodresults are obtained with empty tubes. Other catalysts such as aluminumchloride, ferric chloride, zinc chloride, antimony trichloride andbismuth chloride are also without apparent eflect on the pyrolysisoi-the chloronitriles.

The following examples will illustrate the invention:

Example 1.--0ne mol of a-chloropropionitrile .was passed through a 1"Pyrex tube having a refluxed with sodium bicarbonate solution and.

then distilled. 38.2% of the m-chloropropionitrile was consumed of which69.6% (26.6% of the a-chloropropionitrile feed) was recovered asacrylonitrile. All of the undecomposed u-ChlOlO- propionitrile wasrecovered.

Example 2.The procedure of Example 1 was repeated using a Pyrex tubepacked with pieces of quartz. 47.5% of the u-chloropropionitrile wasconsumed of which 69.2% (32.8% or the a-chloropropionitrile feed) wasrecovered as acrylonitrile.

Example 3.--One mol oi. u-chloropropionitrile was passed through a Pyrextube at the rate of three mols per hour at 600 C. The condensate wastreated with sodium bicarbonate solution and distilled. 34.4% or thea-ChIOIOplODlOIlltI'lIG was consumed of which 75.2% (25.8% of theoc-OhlOlO- propionitrile feed) was recovered as acrylonitrile.

Example 4.0ne mol of u-chloropropionitrile was passed through a Pyrextube at the rate of two mols per hour at 600 C. The condensate wastreated with sodium bicarbonate solution and distilled. 48.1% of thea-chloropropionitrile was consumed of which 81.6% (39.4% of the feed)was recovered as acrylonitrile.

Example 5.--One 1nol of a-chloropropionitrile was passed through aquartz-packed tube of cc. volume at 550 C. at a rate or about one molper hour. The condensate was passed directly intoa solution of sodiumbicarbonate. After all the a-chloropropionitrile had been passed, theorganic layer was separated from the sodium bicarbonate solution anddistilled. 39.4% of the a-chloropropionitrile was consumed 0! which58.8% (23.2% of the feed) was recovered as acrylonitrile. Example 6.Onemol of a-chloropropionitrile was passed through a quartz-packed tube of130 cc. volume at 600 C. at a rate of about one mol per hour. Thecondensate was treated with sodium bicarbonate as described in Example5. 84.7% of the u-chloropropionitrile was consumed of which 62.3% (52.8%of the feed) was recovered as acrylonitrile.

In all of the foregoing examples the unconsumed a-chloropropionitrilewas recovered and used in subsequent experiments as the startingmaterial.

The following examples illustrate the difference in behavior of aandp-chloropropionitrile when treated with alkaline material:

Example 7.A mixture of 30 g. of acrylonitrile, 30 g. ofcz-ChlOl'OPlOPlOllitlilE and 30 g, or p-chloropropionitrile was mixedwith a solution of 40 g. of sodium bicarbonate and 50 g. of distilledwater and then distilled through an efllcient fractionating column. Thefirst fraction distilling at 67-80 C. amounted to 48 g. and contained46.1 g. of pure acrylonitrile which is 96.6% of the theoretical amountassuming that all of the p-chloropropionitrile was converted toacrylonitrile. 28 g. of a-ChlOlOPIODlOl'lltlllt-E or 93.3% of the amountused was recovered in the second fraction distilling between 80 and 90C.

Example 8.A mixture of 0.5 mol each of aand p-chloropropionitrile and200 cc. of water was placed in a flask with phenolphthalein as anindicator. Small portions of 20% sodium hy-' droxide were added and theflask shaken until a permanent slight pink color was obtained. Themixture was then neutralized with hydrochloric acid and 20 g. of sodiumbicarbonate was added. The resulting solution was then fractionallydistilled. 99.7% of the p-chloropropionitrile was recovered asacrylonitrile and 97.3% of the a-ChlOloplODiOl'litlile as such.

Example 9.A mixture of 01- and fl-chloropropionitrile was mixed with aslight excess of cold sodium hydroxide solution, stirred vigorously forone-half hour, then the excess sodium hydroxide was neutralized and themixture was distilled through an efficient fractionating column. Amixture of water and acrylonitrile boiling at 69-'71 C. was firstobtained, and the acrylonitrile layer was equivalent to 94% of thep-chloropro pionitrile used. After the acrylonitrile had been distilledoff, a mixture of a-chloropropionitrile and water boiling at 86-9l C.was obtained containing 94% of the CHaCHClCN used.

Example 10.A mixture of aand p-chloroisobutyronitrile was treated withsodium hydroxide solution in 10% exces of the p-chloroisobutyronitrilecontent and the mixture was vigorously stirred for one hour, whileholding the temperature at 25-30 C. The excess sodium hydroxide was thenneutralized and the oil layer was separated, dried, and fractionallydistilled to separate the methacrylonitrile, B. P. 91 C., from theu-ChlOI'OlSOblltYlOllitl'ilB B. P. 116 C. The recovery was practicallyquantitative.

I claim:

l. The process of preparing an unsaturated nitrile of the formula:

I CHFC-CN from saturated a-chloronitriles of the formula:

R CHr--CN 7 3 from saturated a-chloronitriles of the formula:

wherein R represents a member of the class'consisting of hydrogen andalkylradicals, whichcomprises passing vapors of a saturateda-chloronitrile of the above formula through a pyrolyzing zone at atemperature of about 450 C, to about 700 C.,. condensing the normallyliquid products in the vapors threfrom, thereby forming thecorresponding p-chloronitrile in preponderant amount,dehydrohalogenating said ,B-chloronitrile by treating the condensedproducts with an aqueous alkaline agent from the group consisting ofhydroxides, carbonates, and bicarbonates of sodium, potassium, calcium,and barium in an amount at least equivalent to the'fi-chloronitrile ofthe condensate and any hydrogen chloride which may be dissolved therein,and isolating the resulting unsaturated nitrile by fractionaldistillation.

3. The process of preparing an unsaturated nitrile of the formula:

R CHF-CN from saturated a-chloronitriles of the formula:

wherein R represents a member of the class consisting of hydrogen andalkyl radicals, which comprises passing vapors of a saturateda-chloronitrile of the above formula through a pyrolyzing zone at atemperature of about 450 .C. to about 700 C., condensing the normallyliquid products in the vapors therefrom, thereby forming thecorresponding fl-chloronitrile in preponderant amount,dehydrohalogenating said pchloronitrile by treating the condensedproducts with an aqueous alkaline material from the group consisting ofhydroxides, carbonates, and bicarbonates of sodium, potassium, calcium,and barium in an amount at least equivalent to the p-chloronitrile ofthe condensate and any hydrogen chloride present therein and heating themixture of condensate and aqueous solution'to a temperature up to andincluding the boiling point thereof, neutralizing any excess alkalinematerial, separating an organic layer from the aqueous solution, andisolating therefrom the resulting unsaturated nitrile.

4. The process of preparing an unsaturated.

nitrile of the formula:

bonates, and oicarbonates of sodium, potassium,

calcium, and barium at a temperature-up to and including the boilingpoint of the mixture to dehydrohalogenate at least part of thecondensate, and isolating the resulting unsaturated nitrile.

2. The process of preparing an unsaturated nitrile of the formula:

R CHF-CN a crn=d-oN from saturated a-chloronitriles of the formula:

R CHr-l-CN wherein R represents a member of the class conchioronitrileby treating the condensed products with an aqueous dispersion of analkaline material irom the group consisting of hydroxides, carbonates,and bicarbonates of sodium, potassium, calcium, and barium in an amountat least equivalent to the B-chloronitrile content of the condensate andany hydrogen chloride present therein, and isolating the resultingunsaturated nitrile. Y 5. The process of preparing acrylonitrile froma-chloropropionitrile which comprises passing vapors ofa-chloropropionitrile through a pyrov a 'CHF-CN from saturateda-chloronitriles of the formula:

wherein R represents a member of the classconsisting of hydrogen andalkyl radicals, which comprises passing vapors of a saturateda-chloronitrile of the above formula through a pyrolyz ing zone at atemperature of about 450 C. to about 700 0., condensing the normallyliquid products in the vapors therefrom, thereby formingthecorresponding p-chloronitrile in preponderant amount,dehydrohalogenating said 5- chloronitrile by treating the condensedproducts with a solution of sodium hydroxide in an amount at leastequivalent to the p-chloronit'rile oi the condensate and any hydrogenchloride dissolved therein, andrisolating the resulting unsaturatednitrile by fractional distillation.

'7. The process of preparing acrylonitrile from a-chloropropionitrilewhich comprises passing vapors of a-chloropropionitrile through apyroly'zing zone at about 575 C. to about 625 0., condensing thenormally liquid products in the vapors therefrom, thereby formingp-chloropropionitrile in the condensate, dehydrohalogenating thep-chloropropionitrile in the condensate by treating the latter with anaqueous solution of sodium hydroxide in an amount at least equivalent tothe ,B-chloropropionitrile therein and any hydrogen chloride presenttherein, and isolating the acrylonitrile by fractional distillation.

8. The process of preparing acrylonitrile from a-chloropropionitrilewhich comprises passing vapors of a-chloropropionitrile through apyrolyzing zone at about 575 C. to about 625 C., condensing the normallyliquid products in the vapors therefrom, thereby forming,B-chlcropropionitrile in the condensate, dehydrohalogenating thep-chloropropionitrile in the condensate by treating the latter with anaqueous solution containing an alkaline material from the groupconsisting of the hydroxides, carbonates, and bicarbonates of sodium,potassium, calcium, and barium and heating the resulting mixture up toand including its boiling point, neutralizing any excess alkalinematerial, separating an organic layer from the aqueous solution, andisolating acrylonitrile by fractional distillation of the organic layer.

LE ROY U. SPENCE.

